Advanced MFC Programming

Chapter 10. Bitmap
Now the size of DIB data is already known, we can reallocate the buffers, and call function
::GetDIBits(…) again to receive bitmap data. Finally we need to select the logical palette out of the DC,
and return the handle of the global memory before function exits:
……
}
dwDibLen+=bi.biSizeImage;
hDib=::GlobalReAlloc(hDib, dwDibLen, GHND);
ASSERT(hDib);
lpBi=(LPBITMAPINFO)::GlobalLock(hDib);
ASSERT(hDib);
VERIFY
(
::GetDIBits
(
dc.GetSafeHdc(),
(HBITMAP)pBmp->GetSafeHandle(),
0,
(WORD)bi.biHeight,
(LPSTR)lpBi+sizeof(BITMAPINFOHEADER)+dwSizeCT*sizeof(RGBQUAD),
lpBi,
DIB_RGB_COLORS
)
);
::GlobalUnlock(hDib);
dc.SelectPalette(pPalOld, FALSE);
return hDib;
Using New Functions
Using function CGDIDoc::ConvertDDBtoDIB(…), it is farily easy to save the bitmap into a file. All we
need is to call this function to convert DDB to DIB, add a BITMAPFILEHEADER structure to it, and write the
whole data into a file. In the sample, file saving is implement in function CGDIDoc::Serialize(…):
void CGDIDoc::Serialize(CArchive& ar)
{
if(ar.IsStoring())
{
HGLOBAL hDib;
BITMAPFILEHEADER bmf;
BITMAPINFOHEADER bi;
LPBITMAPINFOHEADER lpBi;
DWORD dwSizeCT;
……
}
hDib=ConvertDDBtoDIB(&m_bmpDraw);
ASSERT(hDib);
bmf.bfType='MB';
bmf.bfSize=sizeof(bmf)+::GlobalSize(hDib);
bmf.bfReserved1=0;
bmf.bfReserved2=0;
lpBi=(LPBITMAPINFOHEADER)::GlobalLock(hDib);
bi=*lpBi;
dwSizeCT=GetColorTableSize(bi.biBitCount);
bmf.bfOffBits=sizeof(bmf)+bi.biSize+dwSizeCT*sizeof(RGBQUAD);
ar.Write((char *)&bmf, sizeof(bmf));
ar.Write((LPSTR)lpBi, bi.biSize+dwSizeCT*sizeof(RGBQUAD)+bi.biSizeImage);
::GlobalUnlock(hDib);
::GlobalFree(hDib);
}
else
In the sample, command File | Save is disabled so that the user can only save the image through File |
Save As command by specifying a new file name. To implement this, UPDATE_COMMAND_UI message
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